Fair Value Measurements (Assets And Liabilities Measured At Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets
Total	$ 714,920	$ 771,275
Liabilities
Long-term debt	44,467	45,378
Contingent purchase consideration	294	898
Total	44,761	46,276
Level 1
Assets
Total	505,414	535,128
Liabilities
Long-term debt	0	0
Contingent purchase consideration	0	0
Total	0	0
Level 2
Assets
Total	208,656	235,300
Liabilities
Long-term debt	44,467	45,378
Contingent purchase consideration	0	0
Total	44,467	45,378
Level 3
Assets
Total	850	847
Liabilities
Long-term debt	0	0
Contingent purchase consideration	294	898
Total	294	898
Money market fund deposits and term deposits
Assets
Cash equivalents	175,411	180,965
Money market fund deposits and term deposits | Level 1
Assets
Cash equivalents	175,411	180,965
Money market fund deposits and term deposits | Level 2
Assets
Cash equivalents	0	0
Money market fund deposits and term deposits | Level 3
Assets
Cash equivalents	0	0
Commercial paper
Assets
Cash equivalents	57,446	78,948
Commercial paper | Level 1
Assets
Cash equivalents	0	0
Commercial paper | Level 2
Assets
Cash equivalents	57,446	78,948
Commercial paper | Level 3
Assets
Cash equivalents	0	0
U.S. Treasury and agency obligations
Assets
Cash equivalents		6,495
Short-term investments	56,203	116,800
U.S. Treasury and agency obligations | Level 1
Assets
Cash equivalents		6,495
Short-term investments	56,203	116,800
U.S. Treasury and agency obligations | Level 2
Assets
Cash equivalents		0
Short-term investments	0	0
U.S. Treasury and agency obligations | Level 3
Assets
Cash equivalents		0
Short-term investments	0	0
Corporate bonds
Assets
Short-term investments	273,800	227,009
Long-term investments and other assets		3,859
Corporate bonds | Level 1
Assets
Short-term investments	273,800	227,009
Long-term investments and other assets		3,859
Corporate bonds | Level 2
Assets
Short-term investments	0	0
Long-term investments and other assets		0
Corporate bonds | Level 3
Assets
Short-term investments	0	0
Long-term investments and other assets		0
Non-U.S. government bonds
Assets
Short-term investments	5,476
Non-U.S. government bonds | Level 1
Assets
Short-term investments	0
Non-U.S. government bonds | Level 2
Assets
Short-term investments	5,476
Non-U.S. government bonds | Level 3
Assets
Short-term investments	0
Commercial paper, not included in cash equivalents
Assets
Short-term investments	145,717	156,321
Commercial paper, not included in cash equivalents | Level 1
Assets
Short-term investments	0	0
Commercial paper, not included in cash equivalents | Level 2
Assets
Short-term investments	145,717	156,321
Commercial paper, not included in cash equivalents | Level 3
Assets
Short-term investments	0	0
Auction rate securities
Assets
Long-term investments and other assets	850	847
Auction rate securities | Level 1
Assets
Long-term investments and other assets	0	0
Auction rate securities | Level 2
Assets
Long-term investments and other assets	0	0
Auction rate securities | Level 3
Assets
Long-term investments and other assets	850	847
Interest rate swap
Assets
Long-term investments and other assets	17	31
Interest rate swap | Level 1
Assets
Long-term investments and other assets	0	0
Interest rate swap | Level 2
Assets
Long-term investments and other assets	17	31
Interest rate swap | Level 3
Assets
Long-term investments and other assets	$ 0	$ 0